"I wasn't looking to leave The Journal per se," she told us. "It was sort of time to mix it up. I've always been curious about doing TV."

Rumors that CNBC was courting Kate, who's been at The Journal for almost 10 years, had been floating around since early March, about a month after she was first approached by the network, she told us.

Kate just returned from maternity leave when CNBC gave her a call. (Disclosure: She is married to my former boss, Kyle Pope, editor of The New York Observer.)

Kate's expertise in covering Wall Street makes her a particularly attractive candidate for a network that appears to be looking to add more reporters who can break news on the air. CNBC approached her around the same time scoop-machine Charlie Gasparino got poached by Fox Business News. (Charlie has since basically disappeared).

Kate's first day will be May 10. She will be reporting to Nik Deogun, The Journal's former deputy managing editor, who left the paper in January to become CNBC's new managing editor.

But first, she is wrapping up a few big pieces for The Journal, Kate told us. She said moving on to TV will be a tough challenge. She's spent her entire career in the print world—first as a reporter at The New York Observer in the late '90s, and then at Time magazine before joining The Journal in 2001.

"The news cycle is gonna be a lot shorter," she said. "In my mind, I'm thinking of it almost like the visual version of being a wires reporter."

Asked about Kate's hire and whether CNBC would be bringing on even more reporters to break news, spokesman Brian Steel would only say: "Our goal is to be fast, accurate, actionable and unbiased."